1. Field of the Invention
The present invention relates to structures for purifying or converting gases, and methods of manufacturing such structures.
2. Discussion of the Background
In recent years, particulates such as soot contained in exhaust gases discharged from internal combustion engines of vehicles such as buses and trucks, and construction machines have raised serious problems as contaminants harmful to the environment and the human body. For this reason, various honeycomb filters, which use a honeycomb structure made of porous ceramics, have been proposed as filters that collect particulates in exhaust gases and purify the exhaust gases.
FIG. 7 is a perspective view that schematically shows one example of a honeycomb structure, FIG. 8(a) is a perspective view that schematically shows a honeycomb fired body forming the honeycomb structure, and FIG. 8(b) is an A-A line cross-sectional view of FIG. 8(a).
In a honeycomb structure 250, as shown in FIG. 7, a plurality of honeycomb fired bodies 240 are combined with one another by interposing an adhesive layer 254 to form a ceramic block 255, and a sealing material layer 253 is further formed on a peripheral face 256 of the ceramic block 255. Moreover, as shown in FIGS. 8(a) and 8(b), each honeycomb fired body 240 has a structure in which a large number of cells 241 are disposed in parallel with one another in the longitudinal direction (the direction shown by an arrow B in FIG. 8(a)), and a cell wall 242 between the cells 241 is allowed to function as a filter. That is, as shown in FIG. 8(b), the ends of either the exhaust gas inlet side or the exhaust gas outlet side of each of the cells 241 formed in the honeycomb fired body 240 is sealed with a plug 246 so that the exhaust gas entering one cell 241 is discharged from another cell 241 after having always passed through a cell wall 242 between the cells 241; thus, when exhaust gas passes through the cell wall 242, particulates are captured by the cell wall 242, so that the exhaust gas is purified.
Here, upon manufacturing a honeycomb structure having the above shape, after a plurality of rectangular pillar-shaped honeycomb fired bodies have been combined with one another to form a rectangular pillar-shaped honeycomb aggregated body having a larger size, a process for cutting the periphery thereof is needed so as to shape the honeycomb aggregated body into a ceramic block having a round pillar shape, with the result that a problem arises in which cut portions generated during this cutting process cause wasteful materials.
In order to solve this problem, Japanese Unexamined Patent Application Publication No. 2004-154718 A (hereinafter referred to as JP2004-154718A) describes a honeycomb filter having a structure that is free from wasteful materials due to cutting processes upon manufacturing. That is, the honeycomb filter described in JP2004-154718A is manufactured by combining a plurality of kinds of honeycomb fired bodies having different shapes by interposing an adhesive layer, without the necessity of the cutting process; thus, the structure of the honeycomb filter is designed in such a manner so as to prevent generation of wasteful materials. The contents of JP2004-154718A are incorporated herein by reference in their entirety.
FIGS. 9(a) to 9(c) show honeycomb fired bodies that form a round pillar-shaped honeycomb filter described in JP2004-154718A. Moreover, FIG. 10 shows a ceramic block formed by combining the honeycomb fired bodies shown in FIGS. 9(a) to 9(c).
The honeycomb filter described in JP2004-154718A is manufactured by using processes in which a plurality of honeycomb fired bodies 220, honeycomb fired bodies 230 and honeycomb fired bodies 240, as shown in FIGS. 9(a) to 9(c), are combined with one another by interposing an adhesive layer 214 to form a ceramic block 215 (see FIG. 10).
The honeycomb fired bodies 220, 230 and 240, shown in FIGS. 9(a) to 9(c), respectively, have a large number of cells 221, 231 and 241, and outer walls 223, 233 and 243 are formed on the peripheral portions of the large number of cells. Thus, the peripheral face 216 of the ceramic block 215 manufactured by using the honeycomb fired bodies having the outer walls on the peripheral portions of the cells is formed into a flat curved face without any step difference (see FIG. 10).
A sealing material layer may be formed on the periphery of the peripheral face 216 of the ceramic block 215 so as to prevent exhaust gases from leaking from the peripheral portion of the honeycomb structure. However, in the case where the sealing material layer is formed on the ceramic block 215, a problem arises in which the sealing material layer is separated from the ceramic block after it has been used as a filter for purifying exhaust gases for a long period of time.